[0001] The present invention relates to the use of a sliding element for seals used for
mechanical seals. More particularly, the invention relates to the use of a sliding
element made from carbon having high degree of hardness which is used for mechanical
seals under a heavy load condition, and which reduces the damage caused by cutting
wear with floating solid foreign matters in sealed fluid or cavitation erosion of
sliding material.
DESCRIPTION OF THE RELATED ART
[0002] JP 03150266 A describes a carbon/carbon composite material useful as a rocket nozzle, brake, etc.
made by mixing 20 to 80 wt% carbon based fiber, 5 to 40 wt% carbonaceous powder and
20 to 50 wt% matrix precurser powder such as powdery phenol resin and subjecting the
mixture to wet type paper making. A plurality of the mixed papers are laminated, heated,
formed and then carbonized and burned in a non-oxidizing atmosphere at 800 to 1000°C
to provide the carbon/carbon composite material. The carbon fibers have a diameter
of 5 to 20 µm, preferably 7 to 13 µm, and a fiber length of 0.3 to 20 mm, preferably
3 to 10 mm.
[0003] JP 63172722 A describes an electroconductive epoxy resin composition. Carbon fiber is mixed with
epoxy resin to make an electrically conductive adhesive. The adhesive is heat treated
at 120°C to cure.
[0004] US 5 242 746 A discloses friction elements of composite carbon-carbon material containing graphitic
fibers.
[0005] GB 1 421 672 A and
GB 1 260 577 A disclose carbon composites obtained by spraying a mixture of carbon fibers, particulate
carbon and binder onto a substrate.
[0006] JPS6295332 discloses a seal made of a mixture of 30-60 wt% carbon powder, 20-40 wt%
resin binder and 10-40 wt% carbon fibers that are mixed to a shape. The fibers have
a thickness of 10-30 microns and a length of 0.1-0.5 mm. The material is used for
a sliding element. The seal is used in a seal assembly. The seal is not fired.
[0007] Generally, carbon sliding materials are often used as seal rings for mechanical
seals to seal the fluid. Between seal sliding faces of the carbon sliding material
and that of mating sliding material, when solid foreign matters such as molding sand,
solder or cutting powder are tramped, floated and invaded in the sealed fluid from
each parts of the system where seals are equipped, the solid foreign matters causes
cutting wear on sliding face of the carbon sliding material. This may lead to the
damage such as extraordinary surface roughness or extraordinary wear on sliding face
and consequently, sealed fluid may leak in cases.
[0008] Also, when the mechanical seals are used under a heavy load condition, by sliding,
sliding faces are mirror surfaced and become in boundary lubrication condition. Lubrication
film between the sliding faces become extremely thin and viscous drag become high,
accordingly, Blister effect (surface blister/ abrasion) on carbon materials may occur.
Also, fluid located to a neighborhood of sliding face may show intense movement and
there are cases when neighborhood of mechanical seals become negative pressure and
cavitation erosion occur on carbon sliding materials. Consequently seal function may
not stably be maintained.
[0009] For above mentioned mechanical seal problems, recently, as sliding materials, the
combination of silicon carbide sliding materials that show high degree of hardness
and excellent wear property may be used.
[0010] However, silicon carbide material is poor in self-lubricant property compared to
carbon material. Accordingly, by sliding under a heavy load condition, sliding faces
become mirror surfaced, fluid film between the sliding faces can not be maintained
and become in boundary lubrication, and along with the effect of sliding heat, the
sliding faces may be secured to each other and seizure may occur in cases. And due
to the sliding heat, secondary seal portion of rubber packing or the like may be damaged
and sealed fluid may leak, consequently seal function may not stably be maintained.
Further, sliding of the two silicon carbide materials, for solid lubrication can not
be expected, if, with any reason, lubrication fluid does not exist in an atmosphere
of seal even for a short time, with the sliding heat, the temperature near the sliding
face show sudden rise and the same inconvenience occur in cases. At the time of initial
running or deactivation of sliding, lubrication film between the sliding faces become
thin and sliding torque may inconveniently rise extraordinarily.
SUMMARY OF THE INVENTION
[0011] An object of the present invention is to provide a seal assembly comprising a sliding
element for seals which has high degree of hardness, excellent wear resistance property
and further, solid lubrication property and their process of manufacturing. The invention
achieving this object is secified in the independent claims.
[0012] The invention provides a seal assembly comprising a sliding element for seals wherein
the sliding element for seals is made by firing a preformed material mainly comprising
25 to 75 weight % carbonaceous impalpable powdery aggregate of non-graphitizing carbon
and/or graphitizing carbon and 20 to 50 weight % synthetic resin as binder, wherein
carbonaceous carbon fibers without surface treatment are blended within the range
of 5 to 25 weight % and inside carbon matrix, said carbon fibers are randomly scattered.
In the present invention, "non-graphitizing carbon" and "graphitizing carbon" show
degree of difficulty for graphitizing. That is, non-graphitizing carbon have difficulty
in graphitizing, to the contrary, graphitizing carbon is easy to graphitize. Non-graphitizing
carbon is exemplified by carbon black, polyvinylidene chloride (PVDC) coal, sugar
coal, cellulose coal, phenol-formaldehyde resin coal and charcoals. Graphitizing carbon
is exemplified by petroleum coke, coal pitch coke, polyvinyl chloride (PVC) coal and
3,5-dimethylphenol formaldehyde resinous coal.
[0013] Moreover, disclosed is a process of manufacturing sliding elements for seals, comprising
the steps of blending source material mainly comprising 25 to 75 weight % carbonaceous
impalpable powdery aggregate of non-graphitizing carbon and/or graphitizing carbon
and 20 to 50 weight % synthetic resin as binder blended with 5 to 25 weight % carbonaceous
carbon fibers without surface treatment, mixing, kneading, molding and firing this
to a predetermined temperature.
[0014] According to the present invention, inside the carbon matrix comprising hard carbonaceous
aggregate, carbonaceous hard carbon fibers are randomly scattered and buried for reinforcement.
Thus, when floating solid foreign matters in sealed fluid invade between sliding faces
of the sliding element and that of mating sliding element, with the effect of reinforced
carbon fibers, intense surface roughness on sliding faces by cutting action of solid
foreign matters is prevented.
[0015] Besides, according to the present invention, the effect of reinforced carbon fibers,
for carbon fibers are carbonaceous and shows high degree of hardness, extend to impalpable
powdery aggregate of non-graphitizing carbon and/or graphitizing carbon used for entire
matrix of carbon material to have high degree of hardness and strength, and prevents
these from falling as impalpable powdery condition. Consequently, wear resistance
property improves considerably and fine seal property can be maintained, and these
are its chief characteristics.
[0016] Also, when seal faces are mirror surfaced by sliding and become nearly in boundary
lubrication condition, with high viscous drag by high viscosity sealed fluid, Blister
effect on sliding faces may occur. However, having carbonaceous aggregate as matrix
and reinforced by carbon fibers that are carbonaceous and a seal assembly comprising
shows high degree of hardness, a seal assembly comprising a sliding element for seals
according to the present invention, by high degree of hardness and strength of carbon
property plus reinforced carbon fibers, the Blister effect can be avoided.
[0017] Likewise, with cavitation erosion that may occur corresponding to the decrease of
fluid pressure near the mechanical seal, having carbonaceous aggregate as matrix and
reinforced by carbon fibers that are carbonaceous and shows high degree of hardness,
a seal assembly comprising a sliding element for seals according to the present invention
can prevent corrosion of carbon surface by the erosion.
[0018] For instance, even soft graphite aggregate comprises carbon matrix which carbonaceous
and hard carbon fibers are scattered inside to reinforce or, to the contrary, even
hard carbonaceous aggregate comprises carbon matrix which soft graphite carbon fibers
are scattered inside, these can not be the countermeasures against contemplate of
the present invention like wear property resistance, Blister resistance or cavitation
erosion resistance. Persistently, a hard carbonaceous aggregate comprising carbon
matrix which carbonaceous and hard carbon fibers are scattered inside to reinforce
sliding element for seals is required.
[0019] Said carbonaceous aggregate has Vickers hardness of 80 or more.
[0020] Further, according to the present invention, for carbon itself has self lubricant
property, even it become in vapor-liquid boundary lubrication between the sliding
faces, the sliding faces are not secured to each other and seizure does not occur.
Likewise, due to the solid lubrication property of carbon, even condition between
the sliding faces come to inexistent of fluid lubrication, sliding heat does not suddenly
rise and also sliding torque does not rise extraordinarily.
[0021] Carbon fibers of the present invention has diameter in a range of from 5 to 30µ m
and length in a range of from 50 to 300µm. When the diameter is smaller than this,
carbon fibers may break during kneading or molding process and the effect of reinforce
inside the carbon matrix may be weakened. When the diameter is larger than this, sliding
torque may rise along with heat generation which causes damage on sliding faces and
consequently sealed fluid may leak in cases. Then, when the length of carbon fibers
are shorter than this, the effect of reinforce inside the carbon matrix may be weakened.
When longer, carbon fibers may break during kneading or molding process, scattering
property may deteriorate, voids may appear on overlapped portion of carbon fibers
inside the carbon matrix and blowholes may appear at angle portion of molded body(sliding
element) in cases.
[0022] Source materials of carbon fibers can be like PAN(polyacrylonitrile) or pitch series
and are not particularly concerned but in order to prevent decrease of hardness, carbon
fibers fired at maximum temperature 1500°C or less is used. When firing temperature
is higher than this, carbon fibers may graphitize and carbon fibers itself deteriorates
its strength. Accordingly, the effect of reinforce as well as improvement in strength
of carbon matrix can not be obtained. Carbon fibers related to the present invention
has 200 or more Vickers hardness and belongs to the category of hard carbon. Further,
carbon fibers related to the present invention is not surface treated and does not
require such process, accordingly lower cost sliding element for seals can be provided.
[0023] Source materials of the present invention mainly comprising 25 to 75 weight % impalpable
powdery aggregate of non-graphitizing carbon and/or graphitizing carbon and 20 to
50 weight % synthetic resin as binder is blended with the range of 5 to 25 weight
% above mentioned carbonaceous carbon fibers without surface treatment.
[0024] Concerning the blend ratio of carbon fibers, when it is lower than above mentioned
range, the effect of reinforced carbon matrix may be weakened and when higher, scattering
property of carbon fibers may deteriorate, voids may appear on overlapped portion
of carbon fibers inside the carbon matrix and blowholes may appear at angle portion
of molded body(sliding element) in cases.
[0025] Concerning the blend ratio of binder, when it is lower than above mentioned range,
aggregate and carbon fibers can not completely be coated and it can not completely
be filled between the two aggregates, furthermore, fluidity of aggregate during the
molding process decreases. To the contrary, when it is higher than above mentioned
range, said defects can be resolved but gas composition generated by thermal decomposition
of binder during firing process often appears and it gives great effect on deformation
or deflation of molded body, further, gas composition may remain in molded body causing
cracks on molded body. According to these combination of adequate blend composition,
blend ratio of aggregate is determined to be 25 to 75 weight %.
[0026] Blending comprising said aggregate, binder and carbon fibers, after the process of
mixing and kneading, has carbon fibers randomly scattered inside the kneaded material.
Further, after molding process, by firing at temperature of 800 to 1500 °C , a seal
assembly comprising a sliding element for seals according to the present invention
which carbon fibers are randomly scattered inside the carbon matrix can be obtained.
[0027] As a binder, blended synthetic resin is not particularly concerned of its composition,
but during kneading process, it requires sufficient wettability with the surface of
aggregate such as non-graphitizing carbon or graphitizing carbon and carbon fibers.
During molding process, it also requires sufficient fluidity inside the metal mold.
Resins that satisfy these may be synthetic resins such as phenolic resin, epoxy resin,
furan resin, polyester resin, and naphthalene resin. One or more kinds from these
resins can be picked and used.
[0028] The obtained carbon material having high degree of hardness which has aggregate impalpable
powdery aggregate of non-graphitizing carbon and/or graphitizing carbon reinforced
by carbonaceous carbon fibers having high degree of hardness as matrix, according
to the purpose of use, may be added by small amount of mineral additive such as clay
or solid lubricant such as graphite aggregate or molybdenum disulfide.
[0029] A seal assembly comprising a sliding element for seals according to the present invention
is suitably used as mechanical seal for water pump, mechanical seal for compressor
of car air conditioner, mechanical seal for pump of industrial use and mechanical
seal for pump of all purposes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030]
FIG 1 is a graph showing the relation between amount of carbon fibers and carbon material
property according to examples of the invention.
FIG 2 is a figure showing a testing machine of wear resistance by foreign material
used in examples of the invention.
FIG 3 is a graph showing the relation between Vickers hardness and wear volume fraction
according to examples of the invention.
FIG 4 is a figure showing a evaluation testing machine for cavitation erosion used
in examples of the invention.
FIG 5 is a figure showing ratios of weight decrease and sample forms after the evaluation.
FIG 6 is a figure showing amount of leakage and form of sample sliding faces after
the evaluation.
FIG 7 is a figure showing configuration of sample sliding faces after the evaluation.
EXAMPLES OF THE INVENTION
[0031] Followings are the examples of the present invention specifically described.
Example 1
[0032] 69 weight % non-graphitizing carbon(aggregate) and 26 weight % thermosetting phenolic
resin(binder) are blended and this is blended with 5 weight % carbon fibers of PAN
series having 15µm diameter and 130µm length. After each treatment of mixing, kneading,
grinding, molding and firing was done to this, seal ring of mechanical seal for sample
was produced. Note that carbon fibers of PAN series with 900 °C maximum temperature
of heat treatment and 250 Vickers hardness was used.
[0033] Vickers hardness(hardness of carbon matrix) and apparent specific gravity of obtained
seal ring were measured. Blend ratio of these composition and material characteristics
of samples are shown in Table 1.
Example 2
[0034] Seal ring was produced under the same condition as example 1 except 65 weight % non-graphitizing
carbon and 30 weight % thermosetting phenolic resin were used. Vickers hardness(hardness
of carbon matrix) and apparent specific gravity of obtained seal ring were measured.
Blend ratio of these composition and material characteristics of samples are shown
in Table 1.
Example 3
[0035] Seal ring was produced under the same condition as example 1 except 62 weight % non-graphitizing
carbon, 28 weight % thermosetting phenolic resin and 10 weight % carbon fibers of
PAN series were used. Vickers hardness(hardness of carbon matrix) and apparent specific
gravity of obtained seal ring were measured. Blend ratio of these composition and
material characteristics of samples are shown in Table 1.
Example 4
[0036] Seal ring was produced under the same condition as example 1 except 54 weight % non-graphitizing
carbon, 26 weight % thermosetting phenolic resin and 20 weight % carbon fibers of
PAN series were used. Vickers hardness(hardness of carbon matrix) and apparent specific
gravity of obtained seal ring were measured. Blend ratio of these composition and
material characteristics of samples are shown in Table 1.
Example 5
[0037] Seal ring was produced under the same condition as example 1 except 50 weight % non-graphitizing
carbon, 30 weight % thermosetting phenolic resin and 20 weight % carbon fibers of
PAN series were used. Vickers hardness(hardness of carbon matrix) and apparent specific
gravity of obtained seal ring were measured. Blend ratio of these composition and
material characteristics of samples are shown in Table 1.
Example 6
[0038] Seal ring was produced under the same condition as example 3 except graphitizing
carbon instead of non-graphitizing carbon was used.
Comparative Example 1
[0039] As a comparative example with respect to examples 1 to 5, seal ring was produced
under the same condition as example 1 except 72 weight % non-graphitizing carbon and
28 weight % thermosetting phenolic resin were used and carbon fibers were not blended.
Vickers hardness(hardness of carbon matrix) and apparent specific gravity of obtained
seal ring were measured. Blend ratio of these composition and material characteristics
of samples are shown in Table 1.
Comparative Example 2
[0040] As a comparative example with respect to examples 1 to 5, seal ring was produced
under the same condition as example 1 except 71 weight % non-graphitizing carbon,
28 weight % thermosetting phenolic resin and 1 weight % carbon fibers of PAN series
were used. Vickers hardness(hardness of carbon matrix) and apparent specific gravity
of obtained seal ring were measured. Blend ratio of these composition and material
characteristics of samples are shown in Table 1.
Comparative Example 3
[0041] As a comparative example with respect to examples 1 to 5, seal ring was produced
under the same condition as example 1 except 42 weight % non-graphitizing carbon,
28 weight % thermosetting phenolic resin and 30 weight % carbon fibers of PAN series
were used. Vickers hardness(hardness of carbon matrix) and apparent specific gravity
of obtained seal ring were measured. Blend ratio of these composition and material
characteristics of samples are shown in Table 1.
[Table 1]
sample |
Comp. Ex. 1 |
Comp. Ex. 2 |
Ex. 1 |
Ex. 2 |
Ex. 3 |
Ex. 4 |
Ex. 5 |
Comp. Ex. 3 |
non-gra phitizing carbon |
72 |
71 |
69 |
65 |
62 |
54 |
50 |
42 |
phenolic resin |
28 |
28 |
26 |
30 |
28 |
26 |
30 |
28 |
carbon fibers |
0 |
1 |
5 |
5 |
10 |
20 |
20 |
30 |
Vickers hardness |
107 |
140 |
220 |
230 |
220 |
220 |
230 |
170 |
apparent specific gravity |
1.42 |
1.43 |
1.42 |
1.44 |
1.40 |
1.39 |
1.41 |
1.39 |
<Evaluation 1>
[0042] Concerning above mentioned examples 1 to 5 and comparative examples 1 to 3, relativity
of blend ratio(weight %) of carbon fibers to Vickers hardness is shown in Figure 1.
As shown in the same figure, by the blend of carbon fibers and by the increase in
blend ratio, Vickers hardness rises. But by further increase in blend ratio of carbon
fibers, Vickers hardness falls. As a result, optimum blend ratio of carbon fibers
are 5 to 20 weight % and with this ratio, Vickers hardness is high and it is preferable
for wear resistance property. Further, for seal ring, preferable Vickers hardness
is 200 or more so that optimum blend ratio of carbon fibers are 5 to 25 weight % as
is shown in the same figure.
[0043] Also, concerning above mentioned examples 1 to 5 and comparative examples 1 to 3,
resistance to wear by foreign material was evaluated. This evaluation of resistance
to wear by foreign material was done as stated below. 0.5 weight % Dust for Industrial
Testing No.8 of JIS Z 8901 "test powders and test particles" and 0.5 weight % alumina
powder(67µm average particle size) are scattered in ion-exchange water and this slurry
solution, at 30-second intervals by 1g, was sprayed to polishing wheel of automatic
polishing testing machine shown in Figure 2. At automatic polishing testing machine
shown in the same figure, polishing wheel revolve at 165 min
-1 on the polishing wheel, carbon material(sample) for evaluation is placed, 20N heavy
bob was loaded and the sample rotate and slide on the polishing wheel. Therefore,
due to the slurry solution which exist among differential gap between the sample and
the polishing wheel, wearing of the sample can be evaluated. Evaluation time was 15
minutes and before and after the evaluation, sample weight was weighed. The weight
difference was converted to volume and treated as wear quantity. Now the evaluation
was done as follows. Relative ratio of sample wear quantity to reference carbon material(blend
ratio of carbon fibers are zero as in comparative example 1) wear quantity was obtained
and decided as index number of wear resistance property.
[0044] When this evaluation of resistance to wear by foreign material was actually done
under above mentioned condition, as shown in figure 1, as the blend of carbon fibers
increase, wear volume fraction decreases and wear resistance property improves. As
the blend of carbon fibers further increases, wear volume fraction increases and wear
resistance property decreases. As a result, optimum blend ratio of carbon fibers are
recognized as 5 to 20 weight %.
<Evaluation 2>
[0045] Wear resistance property of carbon material related to the present invention was
relatively evaluated from that of other materials and its position was confirmed by
said evaluation of resistance to wear by foreign material.
[0046] As evaluation samples, example 3 of table 1 and existing carbon material A and B
of conventional carbon material with good market performance are used. Further, as
other materials, silicon carbide A by normal pressure sintering, silicon carbide B
by reaction sintering, and silicon carbide C and D with remained carbon are used.
Vickers hardness and apparent specific gravity of these carbon materials A and B and
silicon carbide A to D are shown in table 2. Relativity of wear volume fraction to
Vickers hardness is shown in Figure 3.
[Table 2]
sample |
carbon A |
carbon B |
silicon carbide A |
silicon carbide B |
silicon carbide C |
silicon carbide D |
Vickers hardness |
107 |
73 |
2200 |
1400 |
870 |
200 |
apparent specific gravity |
1.55 |
1.60 |
3.04 |
3.05 |
2.60 |
2.30 |
[0047] As is shown in Figure 3, silicon carbide with high Vickers hardness have low wear
volume fractions. When Vickers hardness is higher than 200, wear volume fractions
are small but as Vickers hardness decreases lower than 200, the tendency of increase
in wear volume fractions can be observed. That is, for wear resistance property of
this evaluation condition, materials having high degree of hardness such as silicon
carbide are not required. Materials with 200 or more Vickers hardness are well contented
for wear resistance property.
<Evaluation 3>
[0048] As an evaluation for cavitation erosion, by using ultrasonic homogenizer shown in
figure 4 and keeping 25 to 30 °C water temperature in ion-exchange water, horn was
vibrated at 80µm amplitude and 20 kHz frequency and ultrasonic wave was irradiated
to sample. After 10 minutes of this testing time, weight decreased amount was measured
and evaluated. As evaluation samples, example 3 of table 1 and carbon material A and
carbon material B of table 2 were used. The measured ratios of weight decrease and
electron microscope photographs of evaluated samples are shown in Figure 5.
[0049] As shown in Figure 5, carbon fibers blended hard carbon material of example 3 has
lower ratio of weight decrease relatively to those of conventional existing carbon
material A or carbon material B. And under this evaluation condition, it can be said
that this has erosion resistance property.
<Evaluation 4>
[0050] As evaluation of resistance to wear by foreign material according to mechanical seal
sliding, actual testing machine that simulates water pump was used. Then in 50% aqueous
solution of long life coolant(LLC), 3 weight % Dust for Industrial Testing No.3 of
JIS Z 8901 "test powders and test particles", 3 weight % Dust for Industrial Testing
No.8 of those and 3 weight % 100 to 200 µm molding sand were put, maintained at 90°C
and by keeping 0.1MPa sealed pressure, seal property was evaluated for 50 hours at
8000min
-1 rotary speed. As evaluation result, total amount of leakage and preform of sliding
faces after the evaluation were measured. These are shown in Figure 6.
[0051] As evaluation samples, example 3 of table 1 and carbon material A, carbon material
B and silicon carbide A of table 2 were used for seal ring of mechanical seals for
water pump. And as mating ring of mating sliding material, silicon carbide A was used.
[0052] As shown in Figure 6, though carbon fibers blended hard carbon material of example
3 is little inferior to silicon carbide A in wear resistance property, extreme wear
or extreme leakage do not occur like conventional existing carbon material A or carbon
material B. Accordingly, resistance to wear by foreign material and seal property
as mechanical seal are well contented for their functions.
<Evaluation 5>
[0053] As evaluation of resistance to Blister property according to mechanical seal sliding,
actual testing machine that simulates compressor for car air conditioner was used.
Then after compressor oil was applied on seal ring sliding face, by keeping 5MPa pressure
by nitrogen gas, 0 min
-1 to 3600 min
-1 rotary speed was repeated 15 times by a minute cycle. As evaluation result, sliding
face condition after the evaluation was observed and is shown in Figure 7.
[0054] As evaluation samples, example 3 of table 1 and carbon material A of table 2 were
used for seal ring of mechanical seals for compressor of car air conditioner. And
as mating ring of mating sliding material, silicon carbide A was used.
[0055] As shown in Figure 7, Blister occurred on conventional existing carbon material A,
to the contrary, Blister did not occur on carbon fibers blended hard carbon material
of example 3. And under this evaluation condition, it can be said that this is well
contented for Blister resistance property.
[0056] Concerning said example 6, in the respect of all the above mentioned evaluationes,
the similar result with example 3 was obtained.
[0057] The effect of the invention is as follows.
[0058] According to the present invention, a seal assembly comprising a sliding element
for seals which has high degree of hardness, excellent wear resistance property and
further, solid lubrication property and their process of manufacturing can be produced.